In modern integrated circuits, semiconductor devices are formed on semiconductor substrates, and are connected through metallization layers. The metallization layers are interconnected to the semiconductor devices through contact plugs. Also, external pads are connected to the semiconductor devices through the contact plugs.
The metallization layers are separated from each other by dielectric layers. Further, the metallization layers are separated from active devices by an inter-layer dielectric (ILD). Conventionally, the dielectric layers, particularly the ILDs, are often formed of boronphosphosilicate glass (BPSG).
FIG. 1 illustrates a conventional structure. Transistors 4, which include gates 16 and source/drain regions 14, are formed at the surface of semiconductor substrate 2. Inter-layer dielectric (ILD) 10 is formed on transistors 4. Contact plugs 6 are formed in ILD 10 to electrically connect source and drain regions 14 and gates 16 to metal lines 7 in metallization layer 8. Typically, the formation of contact plugs 6 includes forming openings in ILD 10, and then filling the openings with tungsten plugs. A single damascene process is then performed to form metallization layer 8.
With the down-scaling of integrated circuits, the formation of ILD 10 experiences shortcomings. Due to the increase in the aspect ratio of the gaps between transistors 4, the gap filling of ILD 10 becomes increasingly difficult. Particularly, at the top corners 18 of the gate structures, BPSG tends to be deposited faster than in the middle region between gates 16, hence void 11 may be generated. This situation becomes worse in integrated circuits formed using 90 nm technology or below. Also, boron and phosphorous tend to accumulate in the bottom portions of the BPSG ILD 10. In the etching of ILD 10 for forming contact openings, lateral etching may result in the bottom portions of the BPSG ILD 10. In addition, boron and phosphorous may penetrate into devices, resulting the electrical property shift and even the failure of the devices.
Accordingly, what is needed in the art is a new dielectric structure and formation methods for solving the above-discussed problems.